1. Technical Field
The present invention—involving bookbinding units that form encased booklets by binding into coversheets inner-leaf sheets that have been collated into bundles—relates to improvements in control schemes for controlling bookbinding processes according to sheet-bundle thickness.
2. Description of the Related Art
Bookbinding units that in general collate into bundles sheets that have been printed in a digital printer or other printing machine and encase the bundles in coversheets to form booklets are widely known. With this scheme, inner-leaf sheets collated into a sheet bundle are set into a stack on an inner-leaf tray, and the bundled sheets are conveyed from the tray to an adhesive-application location, and an adhesive (such as a hot-melt adhesive) is applied to a spine-portion endface of the sheets. Meanwhile, a coversheet from a coversheet tray is fed to, and set into place at, a cover-binding location arranged downstream of the adhesive-application location; the spine portion of the inner-leaf sheets, where the adhesive has been applied, is joined to a cover-binding portion of the coversheet in its middle; and thereafter the coversheet is spine-creased and molded in a coversheet pressing means.
Conventionally, as disclosed in Japanese Unexamined Pat. App. Pub. No. 2003-025759, an inner-leaf tray is disposed on one end of the unit, and a cover tray is disposed on the other end. The inner-leaf tray stores collated and stacked inner-leaf sheets (bundles), and the coversheet tray stores a plurality of coversheets of predetermined sizes. The inner-leaf sheets are conveyed in bundle form to a bookbinding processing stage (cover-binding location) situated in the mid-portion of the device, and from the tray the coversheets are conveyed separated into single sheets. To the upstream side of the coversheet binding stage, adhesive tape (or a hot-melt adhesive) is attached to the spine-portion endface of the inner-leaf sheets. In addition, the coversheet binding stage is fitted out with spine-folding press members. Conventional bookbinding units of this sort are known to suffer from the device requiring scaled-up installation space in that, for example, as disclosed in the cited reference, the inner-leaf sheets in bundle form are conveyed with a conveyor mechanism from a sheet supply unit to the bookbinding processing stage. Furthermore, when the three sides (the head, foot and fore-edge portions) of a sheet bundle in booklet form that has been book-forming processed in a bookbinding unit of this sort are trimmed true, the bookbinding unit is equipped with a trimming device that is distinct from the unit, and the trim-finishing is carried out in the trimming device.
Meanwhile, the present applicants have proposed, in Japanese Unexamined Pat. App. Pub. No. 2005-305822 and elsewhere, a unit that continuously bookbinding-processes image-bearing sheets from an image-forming unit. In the publication, a unit is proposed wherein sheets printed with images are collated and stacked in a bookbinding unit connected to a discharge outlet of an image-forming unit. These inner-leaf sheets are conveyed to an adhesive application position by a gripping conveyance means. There a spine portion of the sheet bundle is coated with adhesive. A coversheet is fed from a cover path that is different from the conveyance path for the inner-leaf sheets and set into place in a cover-binding location.
In bookbinding units like that just described, the thickness of the bundle along the spine portion that is bookbinding processed must be detected. For the unit in Japanese Unexamined Pat. App. Pub. No. 2003-025759, a bundle-thickness detection mechanism is disclosed wherein the inner-leaf sheets (text block) are set in a clamping mechanism furnished with a sheet-supply tray, and the bundle thickness of sheets gripped in the clamping mechanism is detected. The unit is configured to place into the binding location a coversheet corresponding to the bundle thickness sensed by the detection mechanism.
Japanese Unexamined Pat. App. Pub. No. 2005-305822 discloses adjusting the application of adhesive by increasing/decreasing the amount based on sheet-bundle thickness information, yet in what way sheet-bundle thickness is detected is not disclosed. In particular, the application amount is modulated by regulating the gap between the sheet bundle and applicator roller based on the thickness information.
As just described, in bookbinding units that form encased booklets by binding inner-leaf sheet bundles in coversheets, detecting the thickness of the inner-leaf sheet bundles and adjusting the adhesive application amount based on the thickness information is known, as is adjusting the position of the coversheets fed to and set into place in the binding location. Such implementations—with a unit configuration, as in the earlier cited Pub. No. 2003-025759, in which the thickness of inner-leaf sheets having been collated onto a tray is detected with the bundle being clamped in a clamping mechanism, and the bundle-thickness information is thereafter employed in the bookbinding processes—carry with them the following problems.
By adopting the structure of the earlier cited reference, in which a clamping mechanism is disposed in the tray where the user sets the sheet bundle to detect the thickness of the sheet bundle, to set the adhesive application amount and coversheet position orientation based the detected thickness, the clamping mechanism cannot accurately detect the sheet bundle thickness if the sheet bundle is not gripped with adequate pressure. The adhesive amount is inaccurate or the coversheet will be displaced if the thickness of the sheet bundle is detected when the clamping mechanism grips the sheet bundle with a weak gripping force. In either case, the quality of the finished booklet will be negatively affected.
When a clamping mechanism is disposed on the tray and a strong pressure is used to the press the sheet bundle, problems occur with users getting their fingers caught in the damper mechanism when setting the sheet bundle on the tray, or the clamping mechanism being damaged if foreign matter enters the tray at the same time as the sheet bundle.
Therefore, when setting the control conditions of the subsequent bookbinding process by detecting the thickness of the sheet bundle, for safety reasons it is preferable that the bundle-thickness detection means be disposed in the unit in a position other than the tray where the inner-leaf sheets are set. However, by disposing this clamping mechanism that detects the sheet bundle thickness inside the unit, new problems arise.
When sheets of a sheet bundle that cannot be clamped are set on the tray, the sheet bundle is conveyed to the clamping mechanism in the unit and the excess sheets can become scattered in the machine. For example, if the preset thickness of the booklet is 50 sheets, and the user mistakenly sets more than 50 sheets on the tray, a jam can occur at the clamping mechanism, and the excess sheets can become scattered.